Which of the following is not true w.rt. K?

Options

A. It indicates the substrate concentration at which half of the maximum velocity of an enzyme catalyzed reaction is attained
B. is not a measure of efficiency of enzyme
C. Value of K of an enzyme remains unchanged in presence of a non competitive inhibitor
D. Allosteric enzymes do not show the typical Michaelis Menten kinetics

Answer

To solve the question "Which of the following is not true with respect to K?", we need to analyze each statement provided in the options regarding the Michaelis-Menten constant (K or Km). Here’s a step-by-step breakdown:

### Step 1: Understand the Definition of K (Km)
K, or the Michaelis-Menten constant (Km), is defined as the substrate concentration at which the rate of the enzyme-catalyzed reaction is half of its maximum velocity (Vmax). This means that Km gives us an idea of how efficiently an enzyme converts substrates into products.

### Step 2: Analyze Each Statement
1. **Statement 1**: "It indicates the substrate concentration at which half of the maximum velocity of an enzyme-catalyzed reaction is attained."
- This statement is **true** because it accurately describes Km.

2. **Statement 2**: "It is not a measure of efficiency of enzymes."
- This statement is **not true**. Km is indeed a measure of enzyme efficiency. A lower Km indicates higher affinity and efficiency of the enzyme for its substrate.

3. **Statement 3**: "The value of K of an enzyme remains unchanged in the presence of a non-competitive inhibitor."
- This statement is **true**. Non-competitive inhibitors do not affect the Km value because they do not change the binding affinity of the enzyme for the substrate.

4. **Statement 4**: "Allosteric enzymes do not show the typical Michaelis-Menten kinetics."
- This statement is **true**. Allosteric enzymes exhibit a different kinetic behavior due to their multiple active sites and subunits.

### Step 3: Identify the Incorrect Statement
From the analysis, the only statement that is not true regarding K (Km) is **Statement 2**: "It is not a measure of efficiency of enzymes."

### Conclusion
The answer to the question is that **Statement 2 is not true with respect to K (Km)**.

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